> The question is, could all of the uses of the MPL
> in Boost (in the Python lib, etc.) be recreated *without* sequence
abstraction?

Oh, the Python lib hardly scratches the surface of what you would want to
do with type sequences. My most serious use of MPL was in another project
whose source is unfortunately never going to be open.

In that project, we were using type lists, and were experiencing
multi-minute compile-times. I was looking forward to experimenting with
some other sequence types. However, in the early stages of development it
was more important to get the implementation right than to worry about
picking the right maximum vector length value, for example ;-). Type lists
seemed like an obvious choice at the time.